Anthocyanin Hybrid Nanopigments from Pomegranate Waste: Colour, Thermomechanical Stability and Environmental Impact of Polyester-Based Bionanocomposites.

Bàrbara Micó-Vicent,Francesca Luzi,Andrea Terenzi,Mahmoud Hamzaoui,Marina Ramos,Stephane Kohnen,María Carmen Garrigós,Franco Dominici,Luigi Torre,Debora Puglia,Valentin Viqueira,Alfonso Jiménez,Etienne Maron

doi:10.3390/polym13121966

Abstract

In the present work, anthocyanin (ACN) hybrid nanopigments were synthetized by using a natural pomegranate dye (PD) and calcined hydrotalcite (HT) and montmorillonite (MMT) nanoclays. A wide colour gamut was obtained with MMT-based nanopigments ranging from reddish to bluish hues caused by structural transformations of ACNs at different pH values. However, a buffer effect was observed with HT obtaining samples a similar final colour regardless of the synthesis conditions. Nanopigments added with a biomordant extracted from pomegranate peels showed a different colour compared to the incorporation of a commercial mordant due to the intrinsic colouring properties of the pomegranate bioadditive. The developed nanopigments were incorporated at 7 wt% loading to produce novel polyester-based bionanocomposites which were characterized in terms of thermal, mechanical and colour properties. The encapsulation of PD into the nanoclays improved its thermal stability, in particular for MMT-based nanopigments. The pH changes observed during the nanofillers synthesis affected the final colour of the MMT-based nanocomposites, inducing a general increase in ∆E* and a decrease in gloss values. Slight improvements were obtained in terms of elastic modulus for MMT-based polymer samples confirming the applicability of the developed bionanocomposites as colouring and reinforcement materials. A very similar environmental profile was obtained for MMT and HT-based nanofillers showing MMT-based nanopigments a slightly better general behaviour. The results of the LCA study evidenced the suitability of the processes used in this work to the circular bioeconomy approach through sustainable food waste management and the production of bioplastics using waste substrates.

Highlights

In the last decades, dyes/pigments and clays were largely used and applied to create coloured design materials
ATM7 nanofiller included the presence of the anionic surfactant cetylpyridinium bromide (CPB) at 5 wt%
The introduction of CPB and the inorganic commercial mordant at 5 wt% was considered in ATM8, while ATM9 included the silane at

Summary

Introduction

Dyes/pigments and clays were largely used and applied to create coloured design materials. Represent an eco-friendly and non-toxic strategy to limit the use of chemical-based products. Polyphenolic dyes extracted from plant leaves and pomegranate rind were used as an alternative eco-friendly approach for nylon dyeing [6]. Natural pigments were added to polymer matrices for colouring purposes, but even for their deodorant, antioxidant and antimicrobial properties [7]. Other studies focused on the dyeing properties of polypropylene and polyamide-based systems prepared by melt compounding the polymer with six-layered clays. Razafimahefa et al found that the introduction of nanoclays improved the dyeing ability of nylon added with dispersed dyes [8,9] and they proposed the production of dyeable polypropylene fibres added with nanoclay particles in the polymer matrix

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